Color cathode ray tube with phosphor strips concave toward vertical center line

ABSTRACT

A color cathode ray tube comprising curved screen including elemental phosphor stripes running cyclically, red, green and blue, a shadow mask adjacent the curved screen and having a plurality of small rectangular apertures, and an electron gun means generating three electron beams arranged in a common plane, said phosphor stripes and the arranging row of the mask apertures are substantially straight on and near the vertical axis of the tube as viewed in the direction of the central axis of the tube and being curved gradually increasing in curvature outwardly in the horizontal axis direction from the center to periphery.

[ 1 June 10, 1975 3,247,412 4/1966 Barneveld et 313/85 S 3,790,839

[ COLOR CATHODE RAY TUBE WITH PHOSPHOR STRIPS CONCAVE TOWARD VERTICAL CENTER LINE [75] Inventors: Takeshi Suzuki; Hiroshi Tanaka, Primary ExaminerRobrt Segal both f Fukaya; Takeo j Attorney, Agent, or Firm-Schuyler, Birch, Swindler, Hiroaki Komatsu, Fukaya, all of McKie & Beckett Japan Tokyo Shibaura Electric Co.,

ABSTRACT Ltd.,

[73] Assignee:

Kawaski-shi, Japan Aug. 30, 1973 Appl. No.: 393,028

[22] Filed: A color cathode ray tube comprising curved screen including elemental phosphor stripes running cyclically, red, green and blue, a shadow mask adjacent the curved screen and having a plurality of small rectangular apertures, and an electron gun means generating [30] Foreign Application Priority Data Aug. 30, 1972 three electron beams arranged in a common plane,

said phosphor stripes and the arranging row of the O M Md 3 S 1W5 3 0 Mm 3 m 1 3 mm Wmm mmr. Ha S I f C smn UIF [56] References Cited UNITED STATES PATENTS 9 Claims, 7 Drawing Figures PATENTEDJUH 10 I975 SHEET FIG. 2

PATENTEDJUH I 0 I975 FIG.5

PATENTEDJUH 10 ms 3.889145 SHEET 4 FIG.7

COLOR CATI-IODE RAY TUBE WITH PHOSPI-IOR STRIPS CONCAVE TOWARD VERTICAL CENTER LINE BACKGROUND OF THE INVENTION This invention relates to an improved color cathode ray tube, and more particularly to a color cathode ray tube in which the improved shadow mask having apertures in the form of slits and the improved screen having smooth edged continuous elemental phosphor stripes are used to give a sufficient electron beam landing tolerance, especially near the edges of the screen.

DESCRIPTION OF PRIOR ART Conventional color cathode ray tubes employ an electroluminescent screen consisting of circular phosphor dots surrounded by light absorbing material, and a shadow mask having a circular aperture corresponding to each triad of phosphor dots as explained U.S. Pat. No. 3,146,368. This screen construction is advantageous to produce an image of enhanced brightness and greater contrast. However, the conventional color cathode ray tubes have some difficulties such as necessity of particular consideration being given to electron beam landing tolerance and necessity of-many complex adjusting attachments, especially beam convergence is complex.

A color cathode ray tube of a new type, called inline gun type has been developed to eliminate such difficulties. It has an image screen including a plurality of phosphor stripes spaced from each other by intermediate stripes made of light absorbing material, a slotted shadow mask adjacent to the screen and an electron gun means for projecting a central beam and a pair of side beams which are disposed in the same plane.

With reference to FIG. 1 of the accompanying drawings which shows a new type color cathode ray tube including a phosphor screen 11 coated on the inner surface of a face plate, a plurality of elemental phosphor stripes are arranged cyclically, green, blue and red color phosphor stripes 12G, 12B and 12R, respectively, and light absorbing stripes 13 are placed between and adjoining the color phosphor stripes 126, 128 and 12R.

The shadow mask 14 of this new tube have a plurality of small rectangular apertures 15 being vertically spaced apart by thin traverse bridge portions 16. These thin bridge portions are significant to form the mask into a spherical contour by pressing. The three electron guns of this tube are placed horizontally adjacent in a so-called in-line configuration.

It has been recognized that such a color cathode ray tube provided with astriped color phosphor screen, and a slotted aperture mask has higher color picture qualities than a conventional color cathode ray tube provided with a circular dot type phosphor screen. Namely, it is capable of reproducing a much brighter image and easy adjusting its color purity.

This newly developed color cathode ray tube, however, has problems in the manufacturing process of the phosphor screen as are mentioned hereinbelow.

The phosphor screen of this new tube is made by a photographic method, using photosensitive resin on the surface of the panel, the above mentioned shadow mask having a plurality of small rectangular beam passable apertures, and using a long light source for projecting bright images of the apertures onto the surface of the panel.

Though there are bridge portions at which the light beam is intercepted in the row of apertures, the phosphor stripe which is to be formed on the panel surface of the bright image of the apertures must be continuous throughout the vertical length of the screen. By using an elongated light source being parallel to the horizontal axis of the tube, a continuous stripelike bright image corresponding to the whole length of the row of the mask apertures is acquired; the dark image of the bridge portion which is projected on the panel by the light beam from an end of the light source is overlapped by a bright image of the light coming through the aperture made from another end of the light source.

In rectangular color cathode ray tubes, the stripes of bright images of the mask apertures produced on the panel as above are sufficiently straight and uniform in width on and near the vertical and horizontal axis of the panel. But, in the corner regions of the panel, the stripes of bright images become considerably zigzagged and ununiform in width. Consequently, phosphor stripes in the corner regions are zigzagged and ununiform in width as shown in FIG. 2, resulting in a decrease in quality of color picture reproduced by the screen.

Especially, the sufficient beam landing tolerance is required near the corner of the screen. Consequently it is very important to eliminate the ununiformity in width of the color phosphor stripes or the light absorbing stripes near the corner of the screen. It was found that the zigzagged form of the stripe images produced on the corner regions of the panel is due to the angular difference between the tangent face of each mask apertures in the lengthwise direction of the aperture rows and the long axis of the light source. As a result, we have improved the color tube by using the improved shadow mask.

SUMMARY OF THE INVENTION According to this invention, in-line gun type color cathode ray tubes of highly improved characteristics can be obtained, the electroluminescent screen having very uniform in width or smooth edged phosphor stripes, electron beam landing tolerance being sufficient over the whole area of the screen, adjustment of the tube being simple and easy, and picture reproduced by the screen being demand of high quality both in colors and whiteness.

Accordingly, an object of this invention is to provide an improved in-line gun type color cathode ray tube which employs a striped phosphor screen.

Another object of this invention is to provide an improved shadow mask.

Another object of this invention is to provide an improved shadow mask in which the slit apertures are arranged in a traversely curved pattern.

Another object of this invention is to provide an improved color cathode ray tube which has sufficient beam landing tolerance near the corners of the screen.

Still another object of this invention is to provide an improved color cathode ray tube is clear and can be easily adjusted the color purity.

BRIEF DESCRIPTION OF THE DRAWINGS following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a fragmentary perspective view of a newly developed color cathode ray tube;

FIG. 2 is an enlarged rear elevational view of the screen of the tube of FIG. 1;

FIG. 3 is a perspective view, partly cut away, of a color cathode ray tube according to this invention;

FIG. 4 is a diagrammatic perspective showing useful in explaining the relation between the arrangement of the mask apertures and the long light source according to this invention;

FIG. 5 is a fragmentary elevational showing the intersection lines on a spherical shadow mask accorcing to FIG. 4',

FIG. 6 is a fragmentary elevational showing the arrangement of the mask apertures according to FIG. 5;

FIG. 7 is a fragmentary enlarged view of the mask apertures according to another embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION For a better understanding of this invention, a description will be given of a color cathode ray tube in which the screen has light absorbing stripes.

FIG. 3 shows a color cathode ray tube of in-line gun type according to this invention. A rectangular-shaped glass panel 31 has, on the inner surface thereof, an electroluminescent screen 32 comprising alternating light absorbing stripes 33 and elemental color phosphor stripes 34, 35 and 36, as well be described in particular hereinafter, arranged in a outwardly curved pattern in a vertical direction or Y-axis of the tube.

A shadow mask 37 of a shape substantially corresponding to the panel is located inside the panel 31. The panel is fixed to a funnel 38 to define an evacuated envelope for the tube.

The funnel 38 has, in its neck portion, an electron gun means 39 for emitting three electron beams 40, 41 and 42 arranged in line in a common horizontal plane containing X-axis of the tube. These electron beams are deflected horizontally and vertically by deflection means 43, and are thereby caused to scan a curved spherical screen 32 through a shadow mask 37.

The shadow mask 37 has a number of small rectangular apertures 44 which are arranged in rows running generally along the vertical direction or Y-axis of the tube. The apertures 44 in each of the rows are aligned lengthwise, as if a very long continuous opening of the same width as that of the apertures is divided into many apertures by very narrow bridge portions 45 of about 0.1 mm in width, for example.

In a conventional shadow mask having slit apertures, each row of the mask aperture are arranged in parallel to the vertical or Y-axis of the tube over the whole effective area of the shadow mask. But, in this invention, the rows of the mask apertures located in the center region of the mask are substantially parallel to the vertical axis of the tube and the remainder of said rows of the mask apertures are traversely curved with a curvature which is gradually increasing outwardly from the center of the mask in horizontal direction or X-axis of the tube.

The light absorbing stripes 33 and the elemental color phosphor stripes 34, 35 and 36 are formed by known light printing methods employing a light beam passing through said the shadow mask 37 The detailed arrangement of the mask apertures will be hereinbelow discussed with reference to FIG. 4 which shows the relationship between the arranging row of the mask apertures and the long light source for forming the screen. The long light source 46 is positioned at the deflection center'of the electron beams as viewed from the panel in the direction of the central axis or Z-axis of the tube. I To make a striped screen, the panel (not shown) with the shadow mask 37 attached thereon is placed with its inner surface downward on the top of an exposing box (not shown). A-light source having a long slit window 46 is provided on the bottom of the box for projecting light onto the inner surface of the panel through the shadow mask 37.

In this invention, the rectangular apertures of the shadow mask are arranged along the intersection lines 48 which are produced with a flat plane 47 containing a long axis L of the light source 46 with the shadow mask 37 FIG. 5 shows the intersection lines 48 as viewed in the direction of the central axis Z of the tube constructed following the directions provided by FIG. 4. The intersection lines 48a produced on and near the Y-axis of the mask are almost straight or parallel to the Y-axis. And the intersection lines 48b produced near the corner or far from the Y-axis are curved outwardly in the X-axis direction with gradually increasing curvature because the mask has an outwardly curved spherical face. 7

The intersection line 48 is an arc of ellipse when viewed from the Z-axis direction is expressed as follows:

Eliminating X by converting (Xo-a),

Xo y 2R Xoa {(R-M V R X0 X0 (.2 2 O where R is the radius of curvature of the spherical mask 37, and M is the distance from the deflection center of the electron beams to the center of the mask as shown in FIG. 4.

FIG. 6 shows an arrangement of the apertures 44 of the shadow mask 37 aligned along the intersection lines as explained in FIGS. 4 and 5.

According to this arrangement of the mask apertures, the light emitted from the light source is projected on the inner surface of the panel along a flat plane containing the intersection line 48 and said long axis L of the light source as explained in FIG. 4.

Therefore, it is impossible to eliminate the ununiformity in width of the bright stripe images due to the angular difference between the tangent face of each mask apertures and the long axis L of the light source.

A striped screen on the panel is made by the light printing method using the above described shadow mask. Therefore, the light absorbing stripes and the elemental color stripes are formed with a pattern corresponding to the intersection lines 48 of the shadow mask in FIG. 6. That is, the stripes are substantially straight on and near the Y-axis of the screen, and are curved gradually increasing in curvature outwardly in the X-axis direction at points removed from the screen center.

FIG. 7 shows the another embodiment of the arrangement of the mask-apertures according to this invention.

The mask 37 has the very narrow bridge portions 50a, 50b which are substantially parallel to the X-axis of the tube to prevent moire phenomena.

Therefore, the mask apertures 52 arranged near the corner of the mask-have a parallelogram configuration.

As above mentioned, according to this invention, the electroluminescent screen has smooth edged continuous color phosphor stripes over the effective area of the screen. And a color cathode tube according to this invention has sufficient beam landing tolerance near the corners of the screen and has higher color picture qualities. While in the above described embodiment the color cathode ray tube has a outwardly curved spherical screen and a spherical shadow mask, the configuration of the screen and the mask may vary from spherical to cylindrical.

In addition to a color cathode ray tube having a light absorbing stripe type screen, this invention is also applicable to other color cathode ray tube in which the screen has only color phosphor stripes.

What is claimed is:

1. A color cathode ray tube comprising a curved screen panel having an inner surface with successive groups of three different elemental color vertical phosphor stripes arranged cyclically therein,

election gun means arrayed on a plane perpendicular to said phosphor stripes for generating three electron beams directed toward said screen for impinging on corresponding ones of said phosphor stripes,

a shadow mask interposed between said gun means and said inner panel surface and having substantially the same curvature as said panel, said mask having vertical rows of beam-passable apertures, said apertures being separated from one another along each row by narrow bridge portions, each of said rows of apertures being associated with one of said groups of phosphor stripes and limiting the illumination thereof by said gun means, said phosphor stripes and associated rows of apertures being substantially straight on and near the vertical axis of the tube as viewed in the direction of the central axis of the tube, and the remainder of said phosphor stripes and associated rows of apertures being outwardly curved in the horizontal axis direction on both sides of the Y-axis of the screen, the color stripes and associated rows of apertures becoming increasingly concave toward the axis of the screen with distance from it. 2. The tube of claim 1 wherein said panel and associated mask are spherical.

3. The tube of claim 2 wherein each of said color 1 phosphor stripes is separated by a light absorbing stripe from the adjacent phosphor stripe.

4. The tube of claim 3 in which the rows of apertures of the mask are arranged along a line of intersection of a flat plane perpendicular to the plane of said gun means and containing the horizontal deflection center line of the electron gun means.

5. The tube of claim 4 wherein the aperture bounding edges of said bridge portions of the shadow mask are substantially parallel to the X-axis of the tube.

6. The tube of claim 1 wherein said panel is substantially cylindrical.

7. The tube of claim 6 wherein each of said color phosphor stripes is separated by a light absorbing stripe from the adjacent phosphor stripe.

8. The tube of claim 7 in which the rows of apertures of the mask are arranged along a line of intersection of a flat plane perpendicular to the plane of said gun means and containing the horizontal deflection center line of the electron gun means.

9. The tube of claim 8 wherein the aperture bounding edges of said bridge portions of the shadow mask are substantially parallel to the X-axis of the tube. 

1. A color cathode ray tube comprising a curved screen panel having an inner surface with successive groups of three different elemental color vertical phosphor stripes arranged cyclically therein, election gun means arrayed on a plane perpendicular to said phosphor stripes for generating three electron beams directEd toward said screen for impinging on corresponding ones of said phosphor stripes, a shadow mask interposed between said gun means and said inner panel surface and having substantially the same curvature as said panel, said mask having vertical rows of beam-passable apertures, said apertures being separated from one another along each row by narrow bridge portions, each of said rows of apertures being associated with one of said groups of phosphor stripes and limiting the illumination thereof by said gun means, said phosphor stripes and associated rows of apertures being substantially straight on and near the vertical axis of the tube as viewed in the direction of the central axis of the tube, and the remainder of said phosphor stripes and associated rows of apertures being outwardly curved in the horizontal axis direction on both sides of the Y-axis of the screen, the color stripes and associated rows of apertures becoming increasingly concave toward the axis of the screen with distance from it.
 2. The tube of claim 1 wherein said panel and associated mask are spherical.
 3. The tube of claim 2 wherein each of said color phosphor stripes is separated by a light absorbing stripe from the adjacent phosphor stripe.
 4. The tube of claim 3 in which the rows of apertures of the mask are arranged along a line of intersection of a flat plane perpendicular to the plane of said gun means and containing the horizontal deflection center line of the electron gun means.
 5. The tube of claim 4 wherein the aperture bounding edges of said bridge portions of the shadow mask are substantially parallel to the X-axis of the tube.
 6. The tube of claim 1 wherein said panel is substantially cylindrical.
 7. The tube of claim 6 wherein each of said color phosphor stripes is separated by a light absorbing stripe from the adjacent phosphor stripe.
 8. The tube of claim 7 in which the rows of apertures of the mask are arranged along a line of intersection of a flat plane perpendicular to the plane of said gun means and containing the horizontal deflection center line of the electron gun means.
 9. The tube of claim 8 wherein the aperture bounding edges of said bridge portions of the shadow mask are substantially parallel to the X-axis of the tube. 